Synthesis, structure and properties of a calcium oxonitridosilicate phosphor showing green or red luminescence upon doping with Eu2+ or Ce3+

Abstract

The phase Li_xCa_16−xSi₁₇N_32−xO_2+x was synthesized by solid-state metathesis at 1050 °C in weld-sealed niobium ampoules. The crystal structure was solved from powder X-ray diffraction data in the space group F3m (a = 14.7391(1) Å, Z = 4); it is closely related to the previously reported structure of Ca₁₆Si₁₇N₃₄. The structure of Li_xCa_16−xSi₁₇N_32−xO_2+x is based on a complex network of [SiN₄] tetrahedra with interstitial voids filled by Ca ions, partially substituted by Li. This Li substitution is charge-compensated by replacement of N by O in the structure. Theoretical calculations confirm that the unit cell volume decreases with increasing stoichiometric factor x. Europium doped samples of this compound show intense Eu²⁺ emission at 536 nm on excitation with near-UV or blue radiation at 350–480 nm. Ce³⁺ doping yields orange to red emission with two broad emission bands at 600 and 665 nm.